To celebrate the 20th anniversary of Half-Life 2, Valve released a documentary in which members of the development team talked about the development of the game and the canceled Half-Life 2: Episode 3.
Half-Life 2: Episode 3 was set in the Arctic and centered around Boreas. Steam engineer David Speyrer recalled how the development team worked on enemy blobs based on isosurface technology, which was later used in Portal for the painting mechanic. The enemy blob could change its shape and it could also be split into smaller blobs that jump like crabs but behave differently. The development team explored all kinds of game ideas with them. For example, they could go through gates, allowing for more dynamic collisions. She focused on combining these creatures and behaviors with other game mechanics to create new, innovative moments.
Steam engineer David Speyrer worked on the ice gun in Half-Life 2: Episode 3. It basically allowed you to create amorphous shapes out of ice. For example, you could build a small ice wall in front of you that was attached to the floor. Alliance soldiers could poke holes in it, causing it to shatter and eventually shatter like glass. This was the main weapon method. You could also use it to build yourself ledges to climb down cliffs. The weapon was also described as a type of “Silver Surfer” mode, in which you could press ice in front of you, run over it, and use it to cross chasms or crevasses.
